Recently, there has been an increase in the need for selective reinforcement, sealing, and resonance frequency alteration of hollow portions of various structural components. As referred to herein, the term “hollow portions” is meant to be expansive and additionally includes channels and spacing between surfaces. Pre-formed reinforcements that utilize expandable formulations, such as heat-activated polymeric foaming materials, have been developed for those purposes.
Although sealing and/or structural reinforcements comprised of heat-activated expandable foams are known in the industry, such conventional reinforcements typically consist of an expandable article comprised of a monolithic structure. Such single component formulations must often integrate two different, but important functions. First, the material must expand to fill a cavity or void. Second, the same material should durably adhere or bond to a portion of the structure being reinforced and/or sealed.
Because two or more important functional tasks are being addressed by a single formulation, the design of single component formulation expandable materials usually requires various compromises and material tradeoffs. For example, a certain ingredient of a single formulation homogeneous matrix might improve the expansion of the formulation, yet hamper the adhesion of the reinforcement to a given structure. Conversely, an ingredient that facilitates adhesion could impede the thermal expansion of the part. Moreover, in a significant number of applications, it is desirable for the reinforcement to function as a resonance frequency dampening device to reduce or eliminate vibration, in addition to acting as a sealant to impede the flow of-water, air and/or vapors through a cavity. Consequently, monolithic materials often tend to impose design constraints.